Thermal processing torches, such as plasma arc torches, are widely used in the heating, cutting, gouging and marking of materials. A plasma arc torch generally includes an electrode, a nozzle having a central exit orifice mounted within a torch body, electrical connections, passages for cooling, and passages for arc control fluids (e.g., plasma gas). Optionally, a swirl ring is employed to control fluid flow patterns in the plenum formed between the electrode and the nozzle. In some torches, a retaining cap can be used to maintain the nozzle and/or swirl ring in the plasma arc torch. In operation, the torch produces a plasma arc, which is a constricted jet of an ionized gas with high temperature and sufficient momentum to assist with removal of molten metal.
Thermal processing torches can be high definition/high performance torches that produce desirable cut qualities, such as narrow cut kerfs and square cut angles. In plasma arc cutting, one effective way of producing the high quality cuts afforded by high definition/high performance torches is to use a smaller nozzle exit orifice diameter and/or higher plasma gas pressure, both of which tend to increase the cut speed. However, as the nozzle exit orifice diameter decreases and gas pressure increases, arc stability becomes unpredictable. Specifically, double arcing can occur or arc can reverberate in the nozzle due to nozzle exit orifice constriction and/or high gas pressure (e.g., created by back pressure from gas exiting the orifice as it passes over material, plate and/or workpiece). For example, during torch operation, the nozzle, including the plasma exit orifice, may be located at different distances (e.g., heights) relative to the workpiece. As the plasma exit orifice moves closer to a solid object (e.g., a workpiece) during torch operation, gas that is expelled through the plasma exit orifice at a high rate contacts the object and the gas can be pushed back toward the plasma exit orifice. The closer the plasma exit orifice is to the object, the more gas is pushed back toward the nozzle and against the continuous gas stream that is attempting to exit the plasma exit orifice, thereby causing reverberation in the nozzle plenum. Often, the reverberation is exacerbated by the use of an irregular workpiece surface during torch operation, where the irregular surface can be caused by, for example, plate debris/slag, weld joint, etc. This can further degrade cut quality and generate double arcing. Cut quality can be compromised in the form of, for example, wavy, choppy and/or serrated cut edges. Thus, systems and methods are needed to improve cut qualities in a thermal processing torch by reducing gas pressure surging in the nozzle plenum of the torch.